ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

Natural Rubber  Silica  Silane  Master­ batch  Easy processing  Compounds Nr-Silica-Masterbatches

Growing requirements of higher fuel The easy Processing Way to High economy increase the pressure on pro- ducers of TBR tires to use silica as a fil- Quality Compounds ler in Natural Rubber compounds. Cur- rently this seems to be the silver bullet to further reduce Rolling Resistance wi- thout compromise in Skid and Wear. 1. Introduction marching modulus and keeping/ en- High quality Natural Rubber com- Natural rubber is the first choice polymer hancing physical properties. For those pounds filled with Silica and Silane in if high tear strength, green strength as who are new to silica compounding, an high dosages are difficult to produce well as green tack are requested. Tire investment into a new mixing line can be with conventional mixing procedures. properties like low wear, good chip & avoided as the material can be used in The Natural Rubber-Silica-Silane Mas- chunk and low rolling resistance can be standard rubber mixing lines as well as terbatches proposed in this paper offer achieved. The outstanding properties on open mills. to produce high quality compounds are the result of its unique, long polymer using shortest mixing cycles and to uti- chains. To improve tear resistance of nat- 2. Natural Rubber-Silica-Masterbatch lize the full potential of this material ural rubber based compounds, up to 15- A masterbatch is a solid product consist- combination. 20 phr silica can be added without the ing of a polymeric carrier material, addi- need of any compatibilizers. Further ben- tives and/ or fillers which are already efits, especially the balance in rolling re- optimally dispersed. sistance, wet skid, and wear can be real- In this particular case the carrier ma- NR-Silica-Masterbatches ized if silica is bound to natural rubber by terial is natural rubber including silica as Ein einfacher Weg der Verar­ coupling agents such as silanes. well as silane. However the compounding of natural Such material has been investigated beitung für qualitativ hoch­ rubber and silica is a big challenge, due earlier, e.g. the Rubber/Filler Composites wertige Gummimischungen to high filler to filler interactions which developed based on NR, E-SBR and SSBR Naturkautschuk  Kieselsäure  Silane  affect the dispersion within natural rub- by Degussa in the late 1990’s and early Masterbatch  einfaches Mischen  ber. Beside this, if it is necessary to mix 2000’s [1]. Advantages in processing and Mischungen high filler volumes into the natural rub- performance have been found already ber, a silanization of the silica becomes then, but commercial success has not Steigende Anforderungen an niedrige essential. This silanization process trans- been realized. During the last 5 years Benzinverbräuche bei LKW erhöhen den forms the rubber mixer into a chemical further developments in the area of Sili- Druck auf Reifenhersteller zur Verwen- reactor, which requires state of the art ca Masterbatches have been conducted, dung von Kieselsäure in Naturkaut- mixing equipment, including exhaust e.g. by INSA, Mexico [2]; the EWE insti- schukmischungen. Nur damit erscheint systems to get rid of volatiles occurring tute of Shanghai [3, 4] and many others. es möglich, weitere Verbesserungen im during the process (dry rubber mixing The production of the Natural Rubber- Rollwiderstand zu erreichen, ohne bei process). A further issue is the long mix- Silica-Masterbatch needs to be explained Bremsverhalten und Abrieb weitrei- ing time which is needed to fully silanize for further understanding. chende Kompromisse eingehen zu müs- the silica, as the high and long-lasting To avoid the silanization within the sen. Qualitativ hochwertige Naturkaut- shear is degrading the polymer chains of mixer, the silica needs to be silanized in a schukmischungen mit Kieselsäure und natural rubber, causing deterioration of previous step. The Behn Meyer Europe Silanen in hohen Dosierungen sind mit its amazing properties. Affinity of impu- GmbH in cooperation with its network of herkömmlichen Verfahren nicht oder rities like phospholipids and proteins, toll producers developed a process to nur sehr aufwändig zu produzieren. Die which are naturally present in natural in diesem Artikel vorgestellten Natur- rubber, to the silica surface further nega- kautschuk-Silica-Silan-Masterbatche tively influence the silanization process bieten die Möglichkeit, in kurzen Misch- of such surface during dry rubber mixing. verfahren zu qualitativ hochwertigen Even if all mixing steps are minutely Mischungen zu gelangen und das volle controlled compounders still face high Potenzial dieser Materialkombination batch to batch variations, high com- auszuschöpfen. pound viscosities as well as changes of Authors the compound properties during storage. To avoid the silanization during mix- Dr. Joachim Bertrand, Johannes ing, long mixing processes and degrada- Bauer, Hamburg, Germany, tion of the natural rubber Behn Meyer Europe GmbH offers a new raw material Corresponding Author: called Natural Rubber-Silica-Masterbatch. Dr. Joachim Bertrand This product shortens the natural rubber Behn Meyer Europe GmbH Figures and Tables: By a kind approval of the authors. and silica mixing process, beside improv- Ballindamm 1, 20095 Hamburg ing the filler distribution, avoiding E-Mail: [email protected]

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surface-modify silica by various silanes. 1 The result is pre-silanized (hydrophobic) silica which is easy to disperse within natural rubber, natural rubber latex and Natural Rubber, Masterbatch other polymers. (Process oil), (coagulated To avoid the degradation of natural Silica and Silane from latex) rubber while mixing it with the pre-si- lanized silica it is necessary to distribute the modified filler in the liquid natural rubber latex. As final step the liquid mix is coagulated and pressed into bales comparable to pure natural rubber. (fig- React Silane Mix of (Mix Process Coagulation, with pure silanized silica oil with drying, bale ure 1) Currently 4 different grades with Silica with NR Latex NR-Latex) forming varying silica- and silane-content are available. Fig. 1: Production Natural Rubber-Silica-Masterbatch

Grade Silica content Silane content 2 in phr in phr NR Si 30 ZO 30 3 NR Si 40 ZO 40 4 NR Si 50 ZO 50 5 NR Si 60 ZO 60 6

To provide the possibility of modifying the content of silica and silane within the natural rubber, Behn Meyer Europe GmbH extended its portfolio by pure pre- silanized silica. As the filler is readily si- lanized it is easily dispersed in the mas- terbatch or other polymers without the need of extending the mixing time.

3. Major Advantages of Natural Rubber-Silica-Masterbatch

Fig. 2: Particle size distribution comparison normal silica filled compound and NR Si MB a. Improved silica dispersion compound. To prove the enhanced silica distribution within the final compound Behn Meyer Europe GmbH (MB) compared a conven- 3 tional compound with 50 phr silica and 5 temperature NR, Silica, Silane Dry mix (3 stage: 8 + 4 + 2 min) phr silane (compound A) and a com- pound mixed with the NR Si 50 ZO in- stead (compound B). As shown on the bilevel picture and particle diameter analysis, the dispersion within com- pound B is improved and the particle di- First MB Second MB Final Batch time (min) ameter on average noticeably smaller. Dispersion phase Silanisation phase (Figure 2) An improved silica dispersion leads to Fig. 3: conventional silica compounding more consistent compounds with better mechanical and physical properties as well as longer lifecycles for the finished starting with the dispersion phase (~2 To avoid this breakdown the use of material. Minutes, only time under full shear Natural Rubber-Silica-Masterbatches is an counted) followed by the silanization excellent alternative. As the silanization is b. Shortening the mixing cycles phase (~10 minutes) and the final batch already finished, a whole mixing step can Additionally to the improved dispersion (~2 minutes), accumulated this results be avoided, furthermore the dispersion of the silica the Natural Rubber-Silica- in an approximate mixing time of 14 phase shortens as well. By using the Natu- Masterbatch shortens the mixing pro- minutes, which also causes breakdown ral Rubber-Silica-Masterbatches the full cess significantly. Normal silica com- of the natural rubber polymer chains. mixing time under shear can be reduced pounding requires 3 stage mixing: (Figure 3) down to 6 minutes. (Figure 4) www.kgk-rubberpoint.de KGK · 01-2 2018 39 ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS

4 cessing additive is added with the chem- temperature icals in 1st stage. (Figure 6) NR-Si-MB very short mix Mixing cycle C is further shortened to (2 stage: 4 + 2 min) 6 minutes in 2 stage mixing, by using the 58% mixing time reduction processing additive together with the 1 stage less Natural Rubber-Silica-Masterbatch in the 240% mixing capacity st 33% less interim storage 1 stage. (Figure 7)

b. Formulation First MB Final Batch To secure comparable results all com- Short No Silanisation phase, time (min) pounds where mixed including the same dispersion only batch compaction raw materials. phase Group 1 is the dry mix group where the silanization is done within the mixer. Fig. 4: Silica compounding with NR Si MB SMR 10 (100 phr) is used alongside BM Silica ZC 185 (60 phr) and Si 69/ TESPT (6 4. Compound properties Mixing cycle A is a traditionally mixed phr) in mixing cycle A. compound with 3 stages, lasting 14 min- Group 2 contains the NR-Si-60 ZO a. Mixing cycles utes. This leaves time to silanize the silica (162,6 phr). This product already con- To compare the compound properties within the mixer if necessary. (Figure 5) tains BM Silica ZC 185 (BET 175-185) as the Natural Rubber-Silica-Masterbatch is Mixing cycle B is shortened by one well sulfur silane (TESPT), so the con- tested against a conventionally mixed stage and takes 10 minutes until dis- tent SMR 10, silica and silane is re- compound in 3 different mixing cycles. charging the final compound. The pro- duced to 0 phr. This group is mixed with mixing cycle A (3 stage mixing) as 5 control group. Group 3 is the first group with re- duced mixing time (mixing cycle B) in- cluding NR Si 60 ZO (162,6 phr). Group 4 has an even shorter process- ing time (mixing cycle C) by using the NR Si 60 ZO. The new Processing Aid Ultra- DFR 900 is added to enhance Master- batch compaction. Remark: In the dry mix 100 phr NR, 60 phr Silica and 6 phr Silane are compared to only 162,6 phr NR-Si-60 ZO, which is Fig. 5: mixing cycle A (conventionally mixing, 3 stages) justified by the content of volatiles that need to be mixed out within the conven- 6 tional compound (Water and Alcohol).

c. Mixing results (visual) In Stage 1, the first 3 groups looked com- parable and show very good results, the 4th group appeared a bit rougher but still very good. Stage 2 delivered very good results for group 1 and 2, both compounds ap- peared smooth and a bit shiny. Fig. 6: mixing cycle B (short mix, 2 stages, processing additive added with chemicals) After final mix (stage 3) all compounds looked nicely and showed a plain surface. 7 Group 1 was somehow tacky and showed some porosity, Groups 2 – 4 were not tacky at all and had no porosity. Whereas with Group 1 a lot of volatiles where cre- ated (water, alcohol), Groups 2 – 4 only lost minor volumes of water (expelled from pores of the silanized silica). VOC’s at Groups 2 – 4 are near to none.

d. Cure characteristics Fig. 7: mixing cycle C (very short mix, 2 stages, processing additive already added with The dry mix (Gr. 1) shows a marching polymer). modulus which is typical if silanization

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of the silica is not finished, even under 8 the long mixing conditions used herein. Group 2, 3 and 4 show no marching modulus, proving the full silanization of the used silica. Group 2 - 4 provide a significantly re- duced viscosity, which is confirmed by a much better mould flow, meaning that the final compound is easier to process e.g. during extrusion, injection- or com- pression- moulding. Even after the very short mixing process of Group 4, viscosi- ty is lower or comparable to the Dry mix reference of Group 1 (Figure 9). e. Physical properties In this comparison the dry mix (group 1, Figure 10) shows a very good physical Fig. 8: formulations overview set, group 2 - 4 a slightly lower TS and EAB level. In further studies this has been different, with a higher level for the mas- Highly interesting are Compression At the same time Rebound improves. We terbatches. However the Reinforcement set results at 100°C: All groups 2 – 4 us- conclude that here the influence of Natu- factor M300 / 100 is improved in all ing the Natural Rubber – Silica – Master- ral Rubber degradation is visible. The groups the Natural Rubber-Silica-Master- batch show a significantly lower CS, with longer the mixing cycle and the higher batch is used in. better values for shorter mixing cycles. the shear conditions (highest with Group

9 Fig. 9: Cure characteristics

10 Fig. 10: Tensile properties

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11

Fig. 11: DMA results

1), the more NR looses its possibilities to g. Conclusion Literature form long range elastic bonds. By using the Natural Rubber-Silica-Mas- [1] U. Goerl, K. H. Nordsiek, Kautschuk Gummi terbatches compounders are able to re- Kunststoffe, 51 (1998) 250. f. Dynamic Mechanical Analysis duce their mixing times by more than [2] US Patent 8357733 B2, 22.1.2013, Wallen et DMA results of this comparison are dis- half. Besides having less process effort, al. (INSA, Cooper Tire & Rubber Company) played in Figure 11. this increases the capacity and reduces [3] Tire Technology Expo Hannover 2016, Meng- Groups 2 – 4 in general and especially the process costs significantly. Jiao Wang “Liquid phase mixing”. Group 4 with the masterbatch mixed at Additionally, the natural rubber keeps [4] Tire Technology Expo Hannover 2016, Meng- shortest mixing time provide the highest its outstanding properties and risky silani- Jiao Wang “Application of EWE compounds Elastic modulus E’ and inelastic E”. To zation during mixing can be avoided com- to Passenger Car Tire Treads”. judge on the potential for Rolling Resis- pletely. This guarantees an easier proce- tance thus the tan delta curve at elevat- dure and improved compound properties. ed temperatures is decisive. VOC production is cut to nearly none. Tan delta for all Groups using the Investments in sophisticated mixing Natural Rubber – Silica – Masterbatch is equipment can be saved, now silica com- lower in the range of 60 – 80°C, which is pounds can be mixed on even elder indicative for the Rolling Resistance of equipment in high quality. TBR tires. Best result, though all groups Compounders of TBR tire as well as are very near to each other, is achieved conveyor belt and anti-vibration com- with Group 3 and the medium short mix- pounds get a versatile raw material to ing cycle. Within this program Group 3 reach the highest goals. provides the best compromise between Processes like continuous mixing on mixing economy (short mixing cycle) and extruder lines with subsequent strip compound quality. At low temperatures winding can be envisaged using the silica Group 3 tan delta turns to be the high- masterbatches. New products are thus est, giving a first indication on good tire possible now. Combinations with surface- skid potential. modified silica grades available from Behn Meyer offer further opportunities.

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